This invention relates to a structure of a light-shielding cloth and a film container, particularly a photographic film container, using the same.
As the containers for a photographic film container, although there are cassettes for sheet films, cartridges for a roll film and the like, all of the containers are provided with a light-shielding member at the slit for extending the film in order to prevent the photographic film from being exposed to light entering there through. When the light-shielding member is a cloth, it is called light-shielding cloth. In typical containers for a light-sensitive strip film, as shown in FIG. 8, a wound light-sensitive strip film, such as photographic film 11, is put in the film container body 13 in a rotatable state, and the slit 14 for extending the light-sensitive film 11 is formed. Light-shielding members for shielding light, such as the light-shielding cloth 15:15 are attached to both of the upper and lower tongue portions 16,16 of the slit 14. The light-shielding cloth is usually colored black in order to ensure the light-shielding ability, and moreover, it is necessary to be soft so as not to damage the photographic film at the time of extending and rewinding it.
The film container disclosed in Japanese Utility model KOKOKU No. 46-20539 is provided with a light-shielding cloth composed of a ground fabric and coreless pile yarn woven thereinto at the slit. The coreless pile yarn is formed from a soft raw yarn having polar groups, such as viscose yarn, acetate yarn or nylon yarn, by crimp processing, and the reverse side of the ground fabric is impregnated with an adhesive in order to fix the pile yarn. Another film container is disclosed in Japanese Patent KOKAI No. 54-36925 wherein the light-shielding cloth is formed by electrostatic flocking.
However, in the case of conventional light-shielding cloth, fraying or falling out of pile yarn occurs during the manufacture of the light-shielding cloth and during extending or rewinding the light-sensitive strip film. Dust from the pile yarn adheres to the surface of the light-sensitive material, and causes trouble in exposure and development. It is also a problem that its manufacture process is complicated and manufacturing cost is expensive. In the case of the light-shielding cloth formed by electrostatic flocking, the workability in the production is inferior due to the use of adhesive, and moreover, the flocked yarn will be easily fall out.
The applicants improved and reported a light-shielding cloth having less troubles, such as fray and falling out, capable of being produced in a relatively simple process and at a low cost (Japanese Utility Model KOKOKU No. 61-34526). The light-shielding cloth has a knitted structure shown in FIGS. 11 and 12, and is formed of a ground fabric 21 having a warp knitted structure formed of filament yarn 23 composed of chain yarn 25 and inlay yarn 26 and a pile portion 22 wherein pile yarn 24 is disposed in parallel to the chain yarn 24, looped and set up. A cross section in the direction perpendicular to the section of FIG. 12 is shown in FIG. 14. The light-shielding cloth is used, for example, in the form shown in FIG. 13, wherein a filler layer 27 and an adhesive layer 28 are provided successively under the ground fabric 21.
A light-shielding cloth structure disclosed in Japanese Patent KOKAI No. 60-208751 uses a conjugate yarn (special yarn) spun of two kind polymers. In another light-shielding cloth disclosed in Japanese Patent KOKAI No. 62-98347, the pile is formed using a high bulky yarn (special yarn).
In general, the light-shielding cloths are dyed using a direct dye, an acid dye, a metal complex dye or the like, and the dye is strongly bound to the fiber of the light-shielding cloth through ionic bonding. Recently, polyester fibers improved in various fiber properties were used for improving the material cost, the light-shielding ability, the film drawing resistance and the like. The light-shielding cloth formed of the polyester fiber is dyed with a disperse dye.
As a recent trend of cameras, they are provided with a high speed winding and rewinding mechanism, and cameras having a winding speed of more than 10 frames per second have been sold. Accompanied with the increased use of the high speed winding camera, a static mark problem occurred due to the generation of static electricity by the friction between the light-shielding cloth attached to the slit of the film container and the photographic film during the operation of the camera. The static electricity was discharged to form exposed spots, and they appeared as the contaminated part, i.e. static marks, by the development. Besides, recent photographic films have a high sensitivity and a high quality, and they are liable to form static marks more than conventional films. As the means to prevent the generation of the static mark, various means have been developed and are disclosed in Japanese Patent KOKAI Nos. 55-129173, 46-28218, 62-286041 and 62-286042.
In the case of the knitted light-shielding cloth disclosed in Japanese Utility KOKOKU Model No. 61-34526, the light-shielding ability was unstable. Moreover, the drawing resistance of the film was relatively great, and the film surface, particularly the photographic emulsion surface, was occasionally damaged. Therefore, when the pile density was increased in order to improve the light-shielding ability, the abrasion troubles increased, and the photographic film could not be delivered in the camera, in the extreme case.
In the case of the light-shielding cloth using the conjugate yarn, the filament was thick, and its bounce impact elasticity was strong. Therefore, the drawing resistance was great. Furthermore, since the conjugate yarn was formed by spinning two kind polymers, it was expensive.
The light-shielding cloth using the high bulky yarn has a problem that, when it was strongly pressed during processing or continuously compressed at the exit, the plush was decreased to degrade the light-shielding ability. Moreover, the light-shielding cloth was expensive due to the price of the yarn.
In the case of the light-shielding cloth formed of the polyester fiber, the dyeing mechanism is different from other conventional light-shielding cloths, and depends on physical bonding, mainly Van der Waals bonds. Therefore, the phenomenon occurred that the bond of the dye is easily released by thermal energy and the like so that it is suspended on the surface of the fiber, called the thermobleeding phenomenon. The thermobleeding phenomenon correlates to the molecular weight of the dye molecule, and a dye molecule having a greater molecular weight induces a greater thermobleeding. Incidentally, disperse dyes are roughly divided into quinone dyes and azo dyes in view of the molecular structure. The quinone dyes are mainly used for light to medium colors because of having relatively a small molecular weight, a small absorption coefficient, a weak fastness of color and a great level dyeing ability, and the azo dyes are mainly used for high concentration dyeing because of having relatively a large molecular weight, a great absorption coefficient, a strong fastness of color and a small level dyeing ability. Thus, the azo dyes were mainly used as the disperse dye for dyeing light-shielding cloths which were colored black, and the thermobleeding occurred greatly due to the large molecular weight of the azo dye molecule. The released dye molecule due to the thermobleeding phenomenon transferred to contaminate the acetate film which was the base film of photographic films under particular environmental conditions, and affected adversely the photographic properties remarkably. For example, when a photographic film cartridge was put in a car while loaded in a camera or packaged in a film case, the photographic film was exposed to a high temperature, and the water content dissolved in the gelatin of the photographic emulsion layer was evaporated and then condensed. The released dye on the surface of the fiber of the light-shielding cloth was transferred to contaminate the photographic film through the condensed water. As mentioned above, in the case of the conventional light-shielding cloth using the black disperse dye, the contamination of the photographic film surface is unavoidable under the particular conditions. In order to solve the above problems, various investigations have been made, but satisfactory results have not been obtained.
As mentioned previously, although various means to prevent the generation of static marks have been developed particularly for the cameras provided with a high speed winding and rewinding mechanism, they were practically unsatisfactory because of losing the softness of the fiber, having a short durability of the antistatic effect or affecting adversely the light-sensitive face of the photographic film. Particularly, in the case of the light-shielding cloth formed of polyester fiber, the treatment with an antistatic agent which is a usual surfactant disclosed in Japanese Patent KOKAI Nos. 62-286041 and 62-286042 was inferior in the durability of the antistatic effect. Moreover, the surfactant was temporarily adhered due to the properties of polyester fiber, and therefore, the surfactant was eluted from the surface of the fiber under an environment where water is present. The eluted surfactant reacted with the photographic emulsion on the film surface, and affected adversely the photographic properties. As the environment where water is present, for example, the photographic film cartridge put in a car mentioned previously corresponds thereto.